Scientific Forecaster Discussion

Area forecast discussion National Weather Service New York New York 617 am EDT sun Sep 15 2019

Synopsis... a weak cold front moves offshore this morning followed by high pressure returning through tonight. Another weak cold front moves through late Monday. High pressure then returns thereafter and remains in control through the end of the week.

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Near term /through tonight/... a weak cold front continues working through the region early this morning. Showers are confined to just offshore of the Long Island coast, and these showers will continue working south and east of the area through sunrise as the cold front moves offshore.

Locally dense fog is also occurring across the interior as the flow behind the front is weak. An Special Weather Statement has been issued to account for the locally dense fog, but visibilities should improve shortly after 8 am as better mixing commences with daytime heating.

High pressure will settle over the area today. There is not much change to the air mass behind the front with just a slight lowering of dew points into the upper 50s and lower 60s. In fact, it will be a few degrees warmer today compared to Saturday as temperatures reach the upper 70s to near 80s degrees.

Cyclonic flow aloft and approaching shortwave energy will gradually increase clouds tonight, especially late for interior locations. Lows temperatures range from the upper 50s inland to the lower and middle 60s most elsewhere.

There is a moderate risk of rip current development at the ocean beaches through this evening.

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Short term /Monday through Monday night/... shortwave energy over southern Ontario and southern Quebec is progged to dive southward around the periphery of a longwave trough centered over the Canadian Maritimes on Monday. This shortwave energy moves into northern New England by Monday afternoon and then off the New England coast Monday night. The shortwave energy will aid in sending a weak cold front into the region on Monday, which quickly passes south by Monday evening. Weak lift and limited moisture continue to be indicated by the models and this makes sense given the northwest flow aloft. A slight chance pop for showers remains in the forecast from the morning inland to the afternoon and evening near the coast. Highs range from the low 70s inland to the middle and upper 70s near the coast. If clouds end up thicker or more widespread ahead of the shortwave energy and front, then highs near the coast may have to be lowered in subsequent forecasts.

High pressure quickly returns behind the front Monday night. Northerly flow behind the front dries out any lingering moisture with skies becoming mostly clear through the night. Lows will range from around 50 degrees across the interior to the upper 50s and low 60s closer to the coast.

There is a moderate risk of rip current development at the ocean beaches on Monday.

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Long term /Tuesday through Saturday/... longwave trough over the Canadian Maritimes will be slow to move east into the North Atlantic Tuesday into Wednesday. However, heights aloft gradually rise and a ridging aloft and at the surface is indicated by the deterministic models and ensemble means to dominate the synoptic pattern through the beginning of next weekend.

Dry weather is expected through the long term. High pressure centered to the north may promote chances of stratus and drizzle for coastal sections Wednesday night through Thursday night. The models are still not indicating this potential. However, will need to monitor trends to see if this changes in future runs since the location of the high to our north would promote an extended period of onshore flow that would enhance these chances. The onshore flow would also limit the mixing height, so expecting highs at or slightly below normal through Thursday. Winds become more offshore for Friday and Saturday, so high temperatures above normal are expected both days.

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Aviation /10z Sunday through Thursday/... a weak cold front moves offshore this morning, followed by high pressure gradually building into the region.

Ceilings early this morning are primarily a mix of MVFR and VFR as the front slowly works across the region, with IFR conditions at a few of the outlying terminals. As the front moves offshore, winds could become light and variable for a couple hours this morning. Otherwise, conditions will improve to VFR within a few hours of daybreak as winds shift to the WNW/NW. Winds then back to the west-southwest this afternoon, with seabreezes expected to develop late in the day at coastal terminals (a few hours earlier along the CT coast). Speeds remain 10 kt or less.

Marine... winds remain rather light today with a weakening pressure gradient and high pressure returning. Ocean seas hover near 4 initially but should subside to about 3 ft through the day. Winds and seas will then remain below Small Craft Advisory levels through Monday.

Offshore flow strengthens a bit Monday night into Tuesday morning before weakening again Tuesday afternoon. Sustained winds may approach 15 kt on the ocean during this time, but gusts remain below 25 kt on all waters. Sub-Small Craft Advisory conditions continue through Wednesday, then winds pick up once again Wednesday night into Thursday with the pressure gradient tightening. Winds should remain below advisory criteria during this period, but ocean swells could increase to 5 ft in association with Humberto and remain elevated through Thursday night.

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Hydrology... no significant hydrologic impacts are currently anticipated through the end of the week.

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Equipment... NYC National oceanic and atmospheric administration weather radio station kwo35 (162.55 mhz) remains off the air.